Polymers
Polymers Polymers are repeating macromolecules , that form long chains of carbon . Classification Natural Polymers Synthetic Polymers Semi Synthetic Polymers Linear Polymers Branched Polymer Cross-linked Polymers Addition Polymers It composes of same or different monomers linked in a long chain . e.g. Polythene , Orlon , Teflon / Condensation Elastomers Fibers Thermoplastic Polymers Thermo-setting Polymers Co-Polymerisation Addition Polymerisation Free Radical Polymerisation 1) Formation of free radicals . This takes place due to breaking of a bond . 2) The free radical molecule reacts with n number of ethylene molecules to form long chains . 3) The chain can be stopped by stopping the supply of ethylene . This step is called as chain terminating step . An initiator is used which undergoes decomposition easily to form free radicals , which initiate the reaction . e.g. benzoyl peroxide , tert - butyl peroxide , acetyl peroxide . Condensation Polymerisation Homopolymers and Heteropolymers Homopolymers - Same Monomers e.g. Polythene , Orlon , Teflon , Polyvinyl chloride , Polystyrene . Heteropolymers - Different Monomers e.g. Nylon-6,6 ; Nylon - 2,6 ; terylene , Buna S , Buna N . Polythene LDPE Ethene is heated at 200o C to 300o C at a pressure 1000 atm . A small amount of oxygen is used as a catalyst . The initiator peroxide is formed during the process due to oxygen . HDPE Ethene is heted 100o C at 6-7 atm . Ziegler - Natta catalyst is used during the process . Ziegler - Natta catalyst i TiCl4 + (C2H5)3Al HDPE is also called as coordination polymer since titanium complex is formed . Orlon (Polyacrylonitrile) ---H2C-(CN)CH2---n prepared from monomer acrylonitrile . used in artificial wool and synthetic carpets . Teflon (Polytetrafluoroethylene) ---F2C-CF2---n Obtained from monomer tertafluoroethylene . Used in oil seals of gaskets and valves , used in non-stick coating on cooking utensils . Nylon Nylon - 6 ---(O=)CH2-(CH2)5-N(H)---n Obtained by heating ε-Caprolactum at a high temperature (533 K) in an inert atmosphere . Nylon-6 is also known as Perlon . Nylon -6,6 ---(H)N-(CH2)6-N(H)-(O=)CH2-(CH2)4-(C=o)---n Prepared from hexamethylenediamine and adipic acid . Nylons '''are used in in making bristles for brushes , fishing nets , bed covers , toys and in textile industry . blended with wool to make socks and sweaters . used in manufacture of colours and climbing ropes . Terylene or Dacron -- CH2 - O - C(=O)-Ar-C(=O) - O ---n (The Benzene is attached to at the para positions ) Polymers having ester linkages are called as polyesters . Terylene is a polyester . Terylene or Dacron is prepared from Ethylene glycol and Dimethylterephthalte (DMT) by heating at 503 K . Terylene is resistant to heat , light ,chemicals ,crease , moths and bacteria . It is used in manufacture of wash and wear fabrics It is blended with cotton to form terrycot and with wool to form terrywool . This increases their resistance to wear and tear . It is used in preparation of fishing nets , ropes , trousers , magnetic tape recorders , tyres ,etc. Bakelite --(OH)Ar(CH2)----n It is prepared from monomers Phenol and Formaldehyde . linear chain of Bakelite is called as Novolac . Low degree polymerization gives soft Bakelite ; used in making glue for binding laminated wooden planks and in varnishes . High degree polymerization gives hard Bakelite ; used in making of electrical switches , plugs , fountain pens , phonograph records , handles of cooker , frying pans , combs . Urea Formaldehyde Polymer Prepared from monomers Urea (NH2-CO-NH2) and Formaldehyde . Used as a moulded plastic . Melamine Formaldehyde Polymer Prepared from monomers Melamine and Formaldehyde . Used in manufacture of crockeries . Natural Rubber It is a natural polymer . It is obtained from latex which is a colloidal solution of of rubber particles in water . Polyisoprene is a linear polymer of isoprene . It contains double bond in each repeating unit . Thus , Polyisoprene shows geometric isomerism . Natural Rubber is cis1,4-polyisoprene . The cis- polyisoprene molecule is held together by weak Van der Waals Forces . Gutta-Percha is trans-1,4-polyisoprene . It has zigzag chains which fit in one another . It is crystalline and non elastic while cis isomer (Natural Rubber) is elastic . Vulcanized Rubber Vulcanization is the process which consists of heating raw rubber with sulphur and an appropriate additive at a temperature ranging between 100o C to 150o C . Natural rubber when mixed with 3 to 5 % of Sulphur , and heated at 100o C to 150o C , forms cross linking of cis - 1,4 - polyisoprene chains through disulphide bonds . Cross linking prevents the polymer from being torn when it is stretched . By controlling the amount of sulphur used in vulcanization , the physical properties of rubber can be altered to suit requirements . When 20-305 sulphur is used , hard rubber is obtained . Rubber made with 3 to 10% sulphur is little hard . '''Buna-S (butadiene rubber) Prepared from monomers buta-1,3-diene and Styrene (Ar-H2C=CH2) Buna-N ''' Prepared from monomers buta-1,3-diene and acrylonitrile '''Neoprene Rubber Prepared from monomer 2-Chlorobuta-1,3-diene Butyl Rubber Prepared from monomer isobutylene and isoprene Biodegradable & Non-Biodegradable Polymers The polymers which are degraded by micro-organisms within a suitable period so that the polymers and thir degraded products do not cause any serious effects on the environment are called biodegradable polymers . PHBV (polyhydroxy butyrate-CO-β-hydroxyvalerate) It is prepared from monomers 3-hydroxy butanoic acid and 3-Hydroxy pentanoic acid . Dextron It is prepared from monomers glycollic acid and lactic acid . Nylon - 2 - Nylon - 6 It is prepared from the monomers glycind and ε-amino caproic acid Other Polymers Dynel : vinyl acetate and acrylonitrile : Human hair wig Glyptal : ethylene glycol and phthalic acid : paints # Thioko Category:Chemistry